Method of measuring interfacial adhesion properties of electronic structures

ABSTRACT

A method for measuring toughness of interfacial adhesion including applying a normal force with a probe to a surface of a coating joined to a major surface of a substrate of an electronic structure, wherein the surface is substantially parallel to the major surface, and applying a lateral force to the coating with the probe by laterally moving a position of the probe relative to the major surface such that the probe forms at least one delaminated region in the coating as the position of the probe moves laterally across the major surface, the delaminated region having a starting point and an ending point. The method further includes measuring a magnitude of the lateral force over time, and determining a toughness of interfacial adhesion between the coating and the major surface based on changes in magnitude of the lateral force as the position of the probe moves from the starting point to ending point.

THE FIELD OF THE INVENTION

The present invention generally relates to a system and a methodemploying an energy-based approach for measuring toughness ofinterfacial adhesion between a coating and electronic structure to whichthe coating has been applied.

BACKGROUND OF THE INVENTION

Devices are commonly coated with thin films and other coatings in orderto enhance their performance and functionality. Such coatings can bebroadly characterized as being either hard coatings or soft coatings.Hard coatings, such as ceramic and diamond-like carbon, for example, areoften applied to cutting tools to enhance their cutting ability anddurability. Soft coatings, such as polymer-based materials, for example,are often applied to medical devices to improve their bio-compatibility.

For purposes of quality and process control, it is desirable to measurethe toughness of the interfacial adhesion, or bond, between the coatingsand substrates. Several testing methods are presently employed tomeasure interfacial adhesion toughness and include the “Pull” or “StudPull” test, the “Four-Point Bending” test, the “Tensile” or “Shear”test, the “Bulge” or “Blister test, the “Laser Impact Spallation” test,the “Indentation” test, and the “Scratch” test. However, there is oftena lack of agreement in the measurements provided by these differenttechniques. Additionally, these techniques are not always effective atmeasuring the interfacial adhesion toughness of coatings applied tosubstrates having non-planar surfaces or flexible structures,particularly when the coatings comprise soft coatings.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a method for measuringtoughness of interfacial adhesion. The method includes applying a normalforce with a probe to a surface of a coating joined to a major surfaceof a substrate of an electronic structure, wherein the surface issubstantially parallel to the major surface, and applying a lateralforce to the coating with the probe by laterally moving a position ofthe probe relative to the major surface such that the probe forms atleast one delaminated region in the coating as the position of the probemoves laterally across the major surface, the delaminated region havinga starting point and an ending point. The method further includesmeasuring a magnitude of the lateral force over time, and determining atoughness of interfacial adhesion between the coating and the majorsurface based on changes in magnitude of the lateral force as theposition of the probe moves from the starting point to ending point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one embodiment of a measuringapparatus according to the present invention.

FIG. 2 is a perspective view of one embodiment of a scratch probeengaging a coating on a device.

FIGS. 3A-3F are cross-sectional views illustrating generally lateralmovement of a scratch probe engaging a coating on a device.

FIG. 4A is a graph of a normal force versus time on a scratch probe.

FIG. 4B is a graph of a lateral force versus time on a scratch probe.

FIG. 5A is a graph of lateral displacement versus time of a scratchprobe.

FIG. 5B is a graph of normal displacement versus time of a scratchprobe.

FIG. 6 is an image of a scratch track in a coating on a device.

FIG. 7 is an enlarged version of the graph of FIG. 4B.

FIG. 8A is a graph of a normal force versus time on a scratch probe.

FIG. 8B is a graph of a lateral force versus time on a scratch probe.

FIG. 9A is a graph of lateral displacement versus time of a scratchprobe.

FIG. 9B is a graph of normal displacement versus time of a scratchprobe.

FIG. 10 illustrates images of multiple scratch tracks in a devicecoating.

FIG. 11 illustrates a graph of lateral force versus time on a scratchprobe and an image of a corresponding scratch track in a coating on adevice.

FIG. 12 is a block diagram illustrating one embodiment of a holdingdevice according to the present invention.

FIG. 13 is a block diagram illustrating one embodiment of a holdingdevice according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. It is to be understood that otherembodiments may be used and structural or logical changes may be madewithout departing from the scope of the present invention. The followingdetailed description, therefore, is not to be taken in a limiting sense,and the scope of the present invention is defined by the appendedclaims.

As described herein, a system and method are provided for measuring thetoughness (energy per unit area) of interfacial adhesion between a thinfilm or coating and an electronic structure to which it is applied. Inone embodiment, the system and method includes applying normal andlateral forces to the coating and substrate and measuring a portion ofapplied energy to determine the work of adhesion to separate ordelaminate a portion of the coating from the electronic structure.

FIG. 1 illustrates one example embodiment of a measuring apparatus 10,according to the present invention, for determining the toughness ofinterfacial adhesion, or work of adhesion (i.e. energy per unit area),between a thin film and an electronic structure device to which it hasbeen applied. Measuring apparatus 10 includes a scratch probe 12, and aplatform 14 configured to hold an electronic structure device 16, or atleast a portion or sample of an electronic structure device 16, having asubstrate 18 to which a coating or thin-film 20, has been applied. Inone embodiment, as illustrated, measuring apparatus 10 further includesa holding device 15 which is selectively coupled to platform 14 andconfigured to hold and secure electronic device structure 16 so that itis not damaged prior to testing.

Examples of electronic structures include semiconductor chips,transistors, layers within electronic structures, insulating materials,microelectromechanical systems (MEMS), nanoelectromechanical systems(NEMS), electronic packaging materials, and electronic processingmaterials.

Measuring device 10 further includes a force sensor 22, a controller 24,and an imaging device 26. Controller 24 is configured to controlmovement of scratch probe 12 in the x, y and z dimensions relative toplatform 14, and to provide a displacement signal 28 representative ofdisplacement of scratch probe 12 in said dimensions from an initialreference point. Force sensor 22 is configured to measure a normal force(F_(N)) 30 and a lateral force (F_(L)) 32 between scratch probe 12 anddevice 16 as scratch probe 12 moves laterally across device 16 at ascratch velocity (V) 34, and to provide a force signal 29 representativeof the measured normal and lateral forces 30 and 32.

Measuring apparatus 10 further includes an imaging device 26 or otherinstrument/device capable of recording or determining the profile orcontour of a test region, such as an optical microscope, a profilometer,a scanning probe microscope (SPM) or an atomic force microscope (AFM),and is configured to provide images of coating 20 and substrate 18 ofsample 16. One example of an optical viewing device suitable to beconfigured for use as imaging device 26 is commercially available underthe trade name Ziess Axio Imager Microscope from Carl ZeissMicroimaging, Incorporated of Thornwood, N.Y., USA. In one embodiment,as will be described in greater detail below, imaging device 26 includesan optical area measurement module 36 for automatically measuring anarea of a user defined region.

Examples of systems similar to measuring apparatus 10 and suitable to beconfigured for use with the present invention are described by U.S. Pat.Nos. 5,553,486 and 5,869,751, both of which are assigned to the sameassignee as the present invention and are incorporated by referenceherein. Another test system suitable to be configured for use with thisinvention is commercially available under the tradename TriboIndenterfrom Hysitron Incorporated of Minneapolis, Minn., USA.

According to one embodiment of the present invention, measuringapparatus 10 is configured to perform an adhesion test, similar innature to a “scratch” test, to measure the interfacial toughness, orwork of adhesion, between coating 20 and substrate 18 to which it isjoined. In one embodiment, controller 24 initially positions scratchprobe 12 proximate to or in contact with coating 20 at a desiredlocation on device 16. For example, in one instance, as illustrated byFIG. 2 below, it may be desirable to position scratch probe 12 away fromedge locations of substrate 18, while in other instances, it may bedesirable to position scratch probe 12 proximate to edges of substrate18.

FIG. 2 is a perspective view illustrating generally portions of oneembodiment of scratch probe 12 in contact with an electronic structuredevice 16. In one embodiment, as illustrated, scratch probe 12 comprisesa cono-spherical probe having a cone-shaped portion 50 having an angle(γ) 52 and a spherical tip 54 having a radius (r) 56 for scratching anddelaminating coating 20 of device 16. In one embodiment, angle 52 isapproximately 60 degrees and radius 56 is approximately 5 micrometers(μm). In one embodiment, angle 52 is approximately 60 degrees and radius56 is approximately 20 μm. Although described primarily herein in termsof having a cono-spherical configuration, scratch probe 12 can be of anyaxis-symmetric configuration such as conical or spherical, for example.

In one embodiment, after initial positioning of scratch probe 12,controller 24 moves scratch probe 12 in the z-direction (downward towardplatform 14 with respect to FIG. 1) so as to cause scratch probe 12 toapply normal force (F_(N)) 30 to device 16. In one embodiment, normalforce 30 comprises a force which increases over time (e.g. a ramp-likeforce). In one exemplary embodiment, as will be described in greaterdetail below, normal force 30 comprises a substantially constant forceor load.

In one embodiment, concurrent with applying normal force 30, scratchprobe 12 and platform 14 are moved laterally to one another(x-direction) at scratch velocity 34 so as to cause scratch probe 12 toapply lateral force (F_(L)) 32 to device 16. In one embodiment,controller 24 causes scratch probe 12 to move laterally across device 16by controlling lateral movement of scratch probe 12 while platform 14remains laterally stationary. Conversely, in an alternate embodiment,controller 24 causes scratch probe 12 to move laterally across device 16by controlling lateral movement of platform 14 while scratch probe 12remains laterally stationary.

As scratch probe 12 moves laterally across device 16, force sensor 22measures normal and lateral forces 30 and 32 between scratch probe 12and device 16 and provides force signal 29 indicative of the measuredvalues of normal and lateral forces 30 and 32. Concurrently, controller24 provides displacement signal 28 indicative of the normal(z-direction) and lateral displacement (x-direction) of scratch probe 12relative to device 16. In one embodiment, controller 24 controls scratchprobe 12 such that scratch probe 12 applies normal force 30 at a desiredconstant load to device 16. As will be described in greater detailbelow, the desired constant normal load may vary depending upon variousfactors associated with coating 20 and may need to be adjusted dependingupon a particular device 16 being tested.

In one embodiment, controller 24 brings normal force 30 from an unloadcondition (i.e. no load) to the desired constant load and maintainsnormal force 30 substantially at the desired constant load for aduration of a scratch operation. At the conclusion of the scratchoperation, controller 24 returns normal force 30 from the desiredconstant load to an unload condition in an unload time. In oneembodiment, the load and unload times each comprise approximately 0.1seconds.

FIGS. 3A-3F are cross-sectional views illustrating portions of device 16being contacted and scratched by scratch probe 12 during a portion of ascratch operation. Referring first to FIG. 3A, as scratch probe 12 moveslaterally across device 16 and normal force 30 is brought to the desiredconstant load, scratch probe 12 begins to penetrate and deform a portionof coating 20, as shown at 60. Additionally, as scratch probe 12 moveslaterally (x-direction as shown), lateral force 32 begins to increase ascoating 20 begins to “bunch up” in front of scratch probe 12, as shownat 62.

With reference to FIG. 3B, as scratch probe 12 continues to movelaterally, lateral force 32 reaches a critical load at which pointcoating 20 is initially fractured or separated from substrate 18, asshown at 64. Also, as indicated at 66, coating 20 continues to pile-upand be pushed ahead of scratch probe 12.

With reference to FIG. 3C, as scratch probe 12 continues to movelaterally across device 16, scratch probe 12 continues to delaminate aportion of coating 20 from substrate 18 and to tear the delaminatedportion of coating 20 from adjacent portions of coating 20 and begins toform a delaminated region having an increasing area, as shown at 67.

With reference to FIG. 3D, as scratch probe 12 continues to movelaterally across device 16, the piled-up coating 20 in front of scratchprobe 12, as illustrated at 70, reaches an amount which can no longer bepushed forward by scratch probe 12. At this point, scratch probe 12 isno longer able to delaminate coating 20 from substrate 18 and the areaof the delaminated region 68 no longer continues to increase. Instead,as scratch probe 12 continues to move laterally, scratch probe 12 beginsto “climb over” piled-up coating 70, as indicated at 72.

With reference to FIGS. 3E and 3F, as scratch probe 12 continues to movelaterally, scratch probe 12 reaches the peak of piled up coating 70, asindicated at 73, and ultimately moves down the opposite side of piled-upcoating 70, as indicated at 74. In one embodiment, as will be describedin greater detail below, the above described process illustrated byFIGS. 3A-3F is repeated, with scratch probe 12 creating a series ofdelaminated areas in coating 20, similar to delaminated region 68, asscratch probe 12 moves laterally across device 16.

As described above, as scratch probe moves across device 16, forcesensor 22 measures normal and lateral forces 30 and 32 between scratchprobe 12 and device 16, and controller 24 measures the normal andlateral displacement of scratch probe 12 relative to device 16. In oneembodiment, as will be described in greater detail below, force sensor22 provides the measured values of normal and lateral forces 30 and 32at force signal 29 in the form of force versus time plots. Similarly, inone embodiment, controller 24 provides measured values of normal andlateral displacement of scratch probe 12 at displacement signal 28 inthe form of distance versus time plots.

Additionally, imaging device 26 provides to-scale images of device 16which illustrate any delaminated regions of coating 20, such asdelaminated region 68 illustrated by FIGS. 3D-3F. In one embodiment, auser defines the boundaries of a delaminated region of coating 20 viameasurement module 36, and measurement module 36 automaticallycalculates the area of the user defined delaminated region.

In one embodiment, as will be described in greater detail below, anamount of “interfacial” energy required to separate or delaminatecoating 20 from substrate 18 to create a delaminated region, such asdelaminated region 68 (see FIGS. 3D-3F), is determined based on aselected portion of the measured values of lateral force 32 provided byforce sensor 22. In one embodiment, as will be described in greaterdetail below, the selected portion of the measured values of lateralforce 32 comprises those values measured by force sensor 22 as scratchprobe 12 moves from a starting point, which corresponds to the initialfracture point of coating 20 from substrate 18 (as illustrated by FIG.3B), to an ending point, which corresponds to the point where scratchprobe 12 no longer delaminates coating 20 from substrate 18 (asillustrated by FIG. 3D).

As will be described in greater detail below with respect to FIG. 7,only the increases in the measured values of lateral force 32 as scratchprobe 12 moves from the starting point to the ending point relative tothe measured value of lateral force 32 when scratch probe is at thestarting point are attributable to the delaminating of coating 20 fromsubstrate 18 in the formation of delaminated region 68. The remainingportion of the measured values of lateral force 32 are attributable totearing the delaminated portion of coating 20 from unaffected portionsof the coating and to friction between scratch probe 12 and substrate18. As such, in one embodiment, the interfacial energy is determinedbased on the increases in the measured values of lateral force 32provided by force sensor 22 as scratch probe 12 moves from the startingpoint to the ending point.

The toughness of interfacial adhesion between coating 20 and substrate18 is then determined by dividing the above determined interfacialenergy by the area of delaminated region 68 as measured by measurementmodule 36. In one embodiment, with reference to FIG. 1, measuringapparatus 10 further includes an analyzer module 38 configured toreceive the displacement signal 28, force signal 29, and the areameasurement from measurement module 36, and configured to determine thetoughness of interfacial adhesion as described above and as will bedescribed in greater detail below with respect to Equations II-IV andFIGS. 4A-7. In one embodiment, analyzer module 38 comprises a portion ofcontroller 24, as illustrated by the dashed lines in FIG. 1.

As briefly described above, in one embodiment, scratch probe 12 is movedlaterally across device 16 such that the process described andillustrated by FIGS. 3A-3F is repeated and a series of delaminatedareas, similar to delaminated region 68, are created as scratch probe 12moves across device 16. In such an embodiment, a toughness ofinterfacial adhesion is determined (as briefly described above) for eachof a selected portion of delaminated areas of the series of delaminatedareas and a toughness of interfacial adhesion between coating 20 andsubstrate 18 is determined based on an average of the toughness ofinterfacial adhesion of the selected portion of delaminated areas.

In summary, by employing a cono-spherical configuration oraxis-symmetrical configuration for scratch probe 12 and the energy-basedmeasurement techniques as described herein, measuring apparatus 10 iswell-suited to determine the toughness of interfacial adhesion of softcoatings applied to hard surfaces, to small surfaces, and to non-planaror other irregular surfaces (e.g. curved surfaces) which do not lendthemselves to be consistently or accurately tested by presently knowntechniques and systems. By determining interfacial energy required todelaminate a portion of the coating from the substrate based on aselected portion of measured values of lateral force as describedherein, measuring apparatus 10 and energy-based measurement techniquesin accordance with the present invention provide accurate and effectivemeasurement of the toughness of interfacial adhesion of soft coatingsapplied to such surfaces relative to known measuring techniques andsystems. In particular, the measuring apparatus and energy-basedmeasurement techniques of the present invention are suitable formeasuring the toughness of interfacial adhesion of coatings applied toelectronic structures.

Furthermore, measuring apparatus 10 and energy-based measurementtechniques according to the present invention do not require speciallyprepared samples or modified devices for testing. As such, measuringapparatus 10 and the energy-based measurement techniques of the presentinvention are suitable for in-situ and on-part/product testing, and maybe part of a laboratory research or a production product testing/qualitycontrol process.

FIGS. 4A-6 below describe an example of the operation of one embodimentof the present invention for determining the toughness of interfacialadhesion between a coating and a substrate to which it has been applied.In the example, device 16 includes a coating 20 comprising a 2 μm thick“parylene C” coating applied to a substrate 18 comprising type 304stainless steel. In this example, substrate 18 comprises a type 304stainless steel tube, as illustrated by FIG. 2. Parylene C is an inert,hydrophobic, optically clear biocompatible polymer coating material usedin a wide variety of industries and applications.

Although described and illustrated herein primarily in terms of a softcoating (e.g Parylene C) on a metal substrate (e.g. stainless steel),other types of coatings and substrates and combinations thereof may alsobe tested. For example, electronic structures having metallic and/ornon-metallic substrates (e.g. copper, aluminum, silicon, siliconnitride, polymers, ceramic, glass) and coatings of materials havinginsulating and/or non-insulating properties (e.g. low-k dielectricmaterials) may also be tested.

In the illustrations described by FIGS. 4A-6 below, normal force 30comprises a substantially constant 15,000 micro-Newton (μN) load appliedto device 16 using a scratch probe 12 having a 60-degree angle 52 and a5 μm tip radius 56 (see FIG. 2) and is moved laterally relative todevice 16 at a constant velocity of approximately 10 μm/second over ascratch distance of approximately 500 μm.

FIGS. 4A and 4B are graphs 76 and 77 respectively illustrating normaland lateral forces 30 and 32 versus time as measured and provided byforce sensor 22 as scratch probe 12 moves laterally (x-direction withrespect to FIGS. 3A-3D) across device 16. FIGS. 5A and 5B are graphs 78and 79 respectively illustrating lateral and normal displacement ofscratch probe 12 versus time as measured and provided by controller 24as scratch probe 12 moves laterally across device 16. With reference toFIG. 5B, it is noted that a normal displacement of “0” at time “0”represents the initial starting point or reference point of tip 54 ofscratch probe 12 at the surface of coating 20 of device 16.

With reference to FIGS. 5A and 5B, when normal force 30 is applied toscratch probe 12 and scratch probe 12 is moved laterally across device16, lateral force 32 begins to increase, as indicated at 80.Concurrently, the normal displacement begins to move downward, asindicated at 82, as scratch probe 12 begins to penetrate coating 20.This corresponds approximately to the position of scratch probe 12 asillustrated by FIG. 3A.

As scratch probe 12 continues to move laterally and downward, lateralforce 32 continues to increase at generally a first slope, as indicatedat 84, until it reaches a critical load at which point coating 20initially “fractures” and separates from substrate 18, as indicated atpoint 86 in FIG. 4B. This corresponds approximately to the position ofscratch probe 12 as illustrated by FIG. 3B.

After the initial fracture of coating 20, lateral force 32 increases atgenerally a second slope, as indicated at 88, as scratch probe 12continues to move laterally and tears the separated coating fromadjoining unaffected areas and delaminates the torn portion of coating20 from substrate 18. This slope change produces a “kink” in the graphof lateral force 32 at point 86 and is referred to and labeled asF_(START). This corresponds approximately to the position of scratchprobe 12 as illustrated by FIG. 3B.

As scratch probe 12 continues to move laterally across device 16,lateral force 32 continues to increase at generally the second slopeuntil an amount of separated coating 20 accumulates in front of scratchprobe 12 such that scratch probe 12 is unable to delaminate anyadditional amount of coating 20. At this point, the normal displacementof scratch probe 12 reaches a local “valley” and begins to move upward,as indicated at point 90 in FIG. 5B. As scratch probe 12 begins to“climb” over the piled-up coating, the progression of delaminationstops. The corresponding lateral force 32 at this point is indicated aspoint 92 in FIG. 4B and is referred to and labeled as F_(END). Thiscorresponds approximately to the position of scratch probe 12 asillustrated by FIG. 3D.

Lateral force 32 continues to increase as scratch probe 12 climbs up thepiled-up coating until it reaches a local peak, as indicated at 94,which is prior to a local upward peak 96 in the normal displacement ofscratch probe 12 when scratch probe 12 reaches a peak of the piled-upcoating. This corresponds approximately to the position of scratch probe12 as indicated by FIG. 3E. As scratch probe 12 crosses the peak of thepiled-up coating and begins to move down the other side, lateral force32 quickly drops, as indicated at 98, as does the normal displacement,as indicated at 100. This corresponds approximately to the position ofscratch probe 12 as indicated by FIG. 3F.

The above described process is repeated as scratch probe 12 continues tomove laterally across device 16 over the 500 μm scratch track resultingin the oscillating nature of the graphs of lateral force 32 and normaldisplacement of scratch probe 12 respectively illustrated by FIGS. 4Band 5B. Each oscillation represents a delamination cycle whichcorresponds to a separate delaminated region (e.g. delaminated region 68illustrated by FIGS. 3D-3F) of a series of delaminated regions ofcoating 20 from substrate 18 created by scratch probe 12 as it moveslaterally across device 16 during a scratch operation. It is noted thatthe overall downward trend of the normal displacement of scratch probe12 illustrated by FIG. 5B results from device 16 being positioned at anangle (i.e. θ+γ/2 ≠90 degrees) with respect to scratch probe 12, asillustrated in FIG. 2.

FIG. 6 is an image provided by imaging device 26 which is representativeof a scratch track 110 caused by application of the 15,000 μN normalforce 30 and lateral movement of scratch probe 12 across device 16 asdescribed above with respect to FIGS. 4A-5B. Scratch track 110 comprisesa series of delaminated regions 112, 114, 116, 118, and 120 wherecoating 20 has been delaminated from substrate 18 by scratch probe 12during a scratch operation, wherein each delaminated region appears asdiamond-like shape which is lighter in color than adjacent areas.

With respect to delaminated region 114, darker regions 122 a and 122 balong the edges of delaminated region 114 illustrate where thedelaminated portion of coating 20 has been torn away from and distortedadjacent remaining areas of coating 20. Darker region 124 illustrateswhere the delaminated portion of coating 20 has piled-up and distortedthe area of coating 20 in front of scratch probe 12 (similar to thatindicated at 70 in FIGS. 3D-3F).

As is typical of each of the delaminated regions illustrated by scratchtrack 110, delaminated region 116 is substantially diamond-like inshape, having a length (d1) 128 and a width (d2) 130. In one embodiment,to measure the area of a delaminated region, such as delaminated region116, a user defines the diamond-like shaped region via imaging device26, the area of which is subsequently calculated by measurement module36. In one embodiment, based on the diamond-like shape, measurementmodule 36 calculates the area based on the following Equation I:

Equation I:A=(d1*d2)/2; where:

-   -   A=area of delaminated region;    -   d1=length of delaminated region; and    -   d2=width of delaminated region.

FIG. 7 is an enlarged version of graph 77 of lateral force 32illustrated by FIG. 4B and describes an example of a process fordetermining an amount of energy required to delaminate a region ofcoating 20 from substrate 18. An oscillation or delamination cycle 140corresponding to delaminated region 116, as illustrated by FIG. 6,begins at point 142. The “kink” in the curve of lateral force 32 fordelamination cycle 140 is indicated at 144 and is labeled as F_(START).The point on the plot of lateral force 32 corresponding to the end ofdelamination for delamination cycle 140 is indicated at 146 and islabeled as F_(END). F_(START) 144 and F_(END) 146 are similar to points86 and 92 previously described with regard to graph 77 of FIG. 4B. Alocal peak of lateral force 32 for scratch cycle 140, as illustrated atpoint 148, corresponds approximately to a position of scratch probe 12before it climbs over and reaches a top of an amount of piled up coating20 in front of scratch probe 12, as illustrated by FIG. 3E. Point 150marks the end of scratch cycle 140 and a beginning point of a nextscratch cycle corresponding to delaminated region 116 (see FIG. 6).

The area below the curve of lateral force 32 from point 142 to F_(START)144 multiplied by scratch velocity (V) 34 substantially represents theenergy supplied by scratch probe 12 to scratch and initially “fracture”coating 20. Energy provided by scratch probe 12 to device 16 in thisregion of the curve for lateral force 32 is also consumed by frictionalforces since scratch probe 12 has relative motion with respect to device16. As such, the energy supplied by scratch probe 12 from point 142 toF_(START) 144 corresponds to scratch probe 12 reaching a positionrepresented by FIG. 3B.

The area below the curve of lateral force 32 between F_(START) 144 andF_(END) 146 multiplied by scratch velocity (V) 34 represents the totalenergy (E_(TOTAL)) supplied by scratch probe 12 to device 16 to tear anddelaminate coating 20 from substrate 18, which corresponds approximatelyto the lateral movement of scratch probe 12 as illustrated generallyabove by FIGS. 3B-3D. It may include the frictional energy consumed dueto relative motion and contact between scratch probe 12 and substrate18. The area below the curve of lateral force 32 after F_(END) 146 topoint 150 multiplied by scratch velocity (V) 34 represents the energysupplied by scratch probe 12 as it climbs “up and over” piled up coating20 in front of scratch probe 12, which corresponds approximately to thelateral movement of scratch probe 12 as illustrated generally above byFIGS. 3E-3F.

The total energy (E_(TOTAL)) supplied by scratch probe 12 betweenF_(START) 144 and F_(END) 146 to create the delaminated region, such asdelaminated region 116, is consumed in various ways and can be generallydescribed by the following Equation II:

Equation II:E _(TOTAL) =E _(INTERFACIAL) +E _(TEARING) +E _(FRICTIONAL); where:

-   -   E_(TOTAL)=total energy to create delaminated region;    -   E_(INTERFACIAL)=energy consumed to delaminate coating from        substrate;    -   E_(TEARING)=energy consumed to tear delaminated coating from        unaffected areas; and    -   E_(FRICTIONAL)=energy consumed by contact and relative motion        between scratch probe 12 and substrate 18.

As described above, the energy supplied by scratch probe 12 from point142 to F_(START) 144 represents the energy required for scratch probe 12to scratch and initially “fracture” coating 20. Once coating 20 beginsto tear away from unaffected adjacent areas of coating 20 at F_(START)144, such as along edges 122 a and 122 b as illustrated with respect todelaminated region 114 of FIG. 6, the energy required to maintaintearing of coating 20, E_(TEARING), remains substantially constant.Additionally, when normal force 30 comprises a substantially constantforce, any frictional energy that may be present between scratch probe12 and substrate 18, E_(FRICTIONAL), also remains substantially constantfrom F_(START) 144 to F_(END) 146.

In light of the above, the increase in the level of lateral force 32from F_(START) 144 to F_(END) 146 represents the force required todelaminate coating 20 from substrate 18 to create delaminated region116. Accordingly, an area of a triangular cross-hatched region 152multiplied by scratch velocity (V) 34 represents the amount ofinterfacial energy, E_(INTERFACIAL), consumed to delaminate coating 20from substrate 18 to create delaminated region 116. In one embodiment,the interfacial energy, E_(INTERFACIAL), is calculated according to thefollowing Equation III: Equation  III:$\quad{E_{INTERFACIAL} = {\sum\limits_{i = F_{Start}}^{F_{End}}\left\lbrack {\left( {x_{i + 1} - x_{i}} \right) \times \left( {\frac{F_{i} + F_{i + 1}}{2} - F_{Start}} \right)} \right\rbrack}}$

-   -   E_(INTERFACIAL)=energy consumed to delaminate coating from        delaminated region;    -   i=individual data point;    -   F_(i)=lateral force at the i^(th) data point;    -   F_((i+1))=lateral force at the i^(th) plus one data point;    -   F_(START)=lateral force at beginning of individual delaminated        region;    -   F_(END)=lateral force at end of individual; delaminated region;    -   x_(i)=lateral displacement at the i^(th) data point and        described by: t_(i)×V;    -   x_(i+1)=lateral displacement at the i^(th) plus one data point        and described by: t_(i+1)×V;    -   t_(i)=time at the i^(th) data point;    -   t_(i+1) time at the i^(th) plus one data point; and V=scratch        velocity.

The toughness of interfacial adhesion (G) between coating 20 andsubstrate 18 of a delaminated region, such as delaminated region 116, isdetermined by dividing the interfacial energy calculated based onEquation III by the area of the delaminated region calculated asdescribed above using FIG. 6 and Equation I. As such, the toughness ofinterfacial adhesion (G) is calculated according to the followingEquation IV:

Equation IV:G=E_(INTERFACIAL) /A; where:

-   -   G=toughness of interfacial adhesion of delaminated region;    -   E_(INTERFACIAL)=interfacial energy associated with delaminated        region;    -   A=area of delaminated region.        It is noted that the toughness of interfacial adhesion is        sometimes also referred to as the “practical work of adhesion.”

In one embodiment, as illustrated by the image of FIG. 6 above, ascratch operation includes applying normal and lateral forces 30 and 32along a desired scratch track to create a series of delaminated regions,such as delaminated regions 112, 114, 116, 118, and 120 along scratchtrack 110. In one embodiment, the toughness of interfacial adhesion (G)is calculated as described above for each of the individual delaminatedregions, and the toughness of interfacial adhesion between coating 20and substrate 18 for device 16 comprises an average of the toughness ofinterfacial adhesion of all of the individual delaminated regions. Inone embodiment, to eliminate any potential anomalies that may beintroduced by initially applying and subsequently removing normal andlateral forces 30 and 32 from device 16, the first and last delaminatedregions of a scratch track are not included when calculating thetoughness of interfacial adhesion between coating 20 and substrate 18based on an average of the toughness of interfacial adhesion of a seriesof delaminated regions. For example, with respect to FIG. 6, thetoughness of interfacial adhesion between coating 20 and substrate 18 isbased on an average of the toughness of interfacial adhesion ofdelaminated regions 114, 116, and 118, with the toughness of interfacialadhesion of delaminated regions 112 and 120 not being included in thecalculation.

Although described above primarily as being a substantially constantforce, normal force 30 may also comprise a force which varies over time.In one embodiment, normal force 30 comprises a ramp-like force whichincreases substantially linearly during a scratch operation. Forexample, FIGS. 8A though 8B respectively illustrate graphs of the normaland lateral forces 30 and 32 with respect to time, and graphs 9A and 9Brespectively illustrate graphs of lateral and normal displacement withrespect to time as scratch probe 12 moves laterally across device 16normal force 30 comprises a ramped force 30. As illustrated by FIG. 8A,normal force 30 is a ramp force which increases from an unload conditionto approximately 15,000 μN as scratch probe 12 moves laterally acrossdevice 16 at a velocity of approximately 10 μm/second.

Similar to that described above with respect to FIGS. 4B and 5B, thegraphs of lateral force 32 and normal displacement illustrated by FIGS.8B and 9B have an oscillating type pattern as scratch probe 12 movesacross device 16, with each oscillation corresponding to an individualdelaminated region. The toughness of interfacial adhesion for anindividual delaminated region is calculated in a fashion similar to thatdescribed above, with the interfacial energy (E_(INTERFACIAL)) beingapproximately equal to the area of a triangular region below the curveof lateral force 32 between F_(START) and F_(END), such as triangularregion 160 between F_(START) and F_(END) 162 and 164 multiplied byscratch velocity (V) 34. The generally upward trend of the graph oflateral force 32 illustrated by FIG. 8B is due generally to increasingfrictional forces between scratch probe 12 and substrate 18 of device 16as normal force 30 increases.

As mentioned above with respect to FIG. 2, a desired load to employ asnormal force 30 so as to effectively delaminate coating 20 fromsubstrate 18 may vary between devices 16 to be tested depending onfactors such as, for example, the mechanical properties of the materialemployed for coating 20, the thickness of coating 20, and the toughnessof interfacial adhesion between coating 20 and substrate 18. However,normal force 30 must be applied at least at a minimum level required tocause coating 20 to delaminate from substrate 18.

In one embodiment, to determine a desired constant scratch load to beutilized for normal force 30, a scratch operation is first performed ondevice 16 using a ramp load for normal force 30, wherein normal force 30is increased from zero to a selected maximum load over the duration ofthe scratch operation. Images of coating 20 provided by imaging device26 and displacement and force signals 28 and 29 respectively provided bycontroller 24 and force sensor 22 are analyzed to approximatelydetermine a minimum level of normal force 30 at which coating 20delaminates from substrate 18. Normal force 30 is then applied atplurality of levels, beginning with the minimum level determined above,and scratch probe 12 is moved at different velocities (see FIG. 1)laterally relative to device 16 so as to create a plurality of scratchtracks so as to determine a desired constant load at which to applynormal force 30 and scratch velocity 34.

In one embodiment, a normal load and velocity which results in scratchprobe 12 generating a scratch track having a desired number ofdelaminated regions over a predetermined track length in coating 20 ofdevice 16 are selected as the desired constant normal load to be appliedto scratch tip 12 for testing the toughness of interfacial adhesionbetween coating 20 and substrate 18 of device 16. In one embodiment, thedesired number of delaminated regions is between three and fivedelaminated regions.

As an example, FIG. 10 illustrates optical micrographs generated byimaging device 26 for various scratch tracks produced in coating 20 of adevice 16 by scratch probe 12 with normal load 30 at different constantnormal loads. Similar to that illustrated by FIG. 6, device 16 includesa coating 20 comprising parylene C and a substrate 18 comprising Type304 stainless steel. Scratch tracks 180, 182, 184, and 186 respectivelyillustrate scratch tracks created with a normal force 32 at a load of 20mN, 25 mN, 30 mN, and 35 mN, with each scratch tracking having a scratchlength of approximately 500 μm. Scratch tip 12 employed to generate thescratch tracks included a spherical tip 54 having a 5 μm radius 56 andwas moved laterally at a scratch velocity 34 of 10 μm/sec.

Each scratch track comprises a series of delaminated regions similar tothat illustrated by FIG. 6, with the series of delaminated regionsforming what is referred to herein as a “bamboo” structure. In theexample illustrated by FIG. 10, a normal load of 20 mN is the minimumforce required to delaminate coating 20 from substrate 18 of theparticular device 16 tested. In one embodiment, where five delaminatedregions is the desired number of delaminated regions to be attained, anormal load of 30 mN corresponding to scratch track 184 would beselected as the desired constant load to employ as normal force 30 fortesting device 16.

It is noted that a number of delaminated regions in a bamboo structureof a given scratch track generally decreases with increasing normalforce, while an area of each of the individual delaminated regionsgenerally increases. Because the area generally increases withincreasing normal force, the toughness of interfacial adhesion, G, asdetermined by Equations III and IV above, remains substantially constantover a range of normal loads. As such, the magnitude of the loademployed by constant normal force 30 does not substantially impactcalculated values of the toughness of interfacial adhesion betweencoating 20 and substrate 18 as long as normal force 30 is at least equalto a minimum scratch load required to fracture and delaminate coating 20from substrate 18.

In one embodiment, in lieu of performing scratch operations at a singledesired constant load, scratch operations are carried out a plurality ofnormal loads, such as illustrated by FIG. 10. In such an embodiment, thetoughness of adhesion of coating 20 to substrate 18 is calculated foreach of the individual delaminated regions of each scratch track, suchas each of the individual delaminated regions of scratch tracks 180,182, 184, and 186, as described above with respect to Equations I, II,and IV. A toughness of interfacial adhesion between coating 20 andsubstrate 18 is then determined by finding an average toughness ofinterfacial adhesion of all delaminated regions of all the scratchtracks.

It is also noted that, through experimentation, scratch velocity 34 wasfound to have negligible impact on calculated values of the toughness ofinterfacial adhesion. It was found that increasing scratch velocity 34results in a decrease in the area of corresponding delaminated region.However, the calculated toughness of interfacial adhesion for a givendevice 16 remained substantially constant at various scratch velocities34 as the proportionality between an area of a delaminated region (seeEquation I) and interfacial energy (E_(INTERFACIAL)) corresponding tothe delaminated region (see Equation III) remains substantiallyconstant.

FIG. 11 illustrates the relationship between lateral force 32 andcorresponding delaminated regions created in coating 20 of a testeddevice 16. FIG. 11 includes a graph 190 of lateral force 32 resultingfrom a scratch probe 12 applying a constant 30 mN normal force to andmoving laterally across device 16 at a scratch velocity of 10 μm/sec. Anoptical micrograph provided by imaging device 26 illustrates acorresponding scratch track 192 comprising a series of delaminatedregions 194, 196, 198, 200, and 202 and which is time-wise aligned withgraph 190.

As illustrated, each oscillation or delamination cycle of lateral force32 of graph 190 corresponds to a delaminated region of scratch track192. For example, a scratch cycle 204 corresponds to delaminated region200 with F_(START) 206 and F_(END) 208 aligning respectively with abeginning point 210 and an ending point 212 of delaminated region 200.The interfacial energy (E_(INTERFACIAL)) required to form delaminatedregion 200 is equal to an area of triangular-shaped region 214multiplied by scratch velocity (V) 34.

FIG. 12 is block diagram illustrating generally one embodiment ofholding device 15 according to the present invention for securing anelectronic structure device 16 during a scratch operation. Holdingdevice 15 includes a platform 220 including a plurality of perforations(illustrated by dashed lines) through platform 220, such as illustratedat 222, and a vacuum system 224. Vacuum system 224 includes a fan 226and a manifold 228. Manifold 228 is coupled to platform 220 so as toform a plenum across all perforations 222, and is connected to fan 226via a vacuum line 230. Fan 226 is configured to draw air throughperforations 222 via manifold 228 and vacuum line 230. When anelectronic structure device 16, such as a silicon wafer, for example, isplace over perforations 222, a vacuum is created which secureselectronic device 16 to platform 220.

FIG. 13 is a block diagram illustrating generally another embodiment ofholding device 15 according to the present invention. As illustrated,holding device 15 comprises a magnetic platform 240 configured tomagnetically hold a plurality of electronic structure devices 16 havingmagnetic metallic substrates 18. In one embodiment, with reference toFIG. 1, controller 24 is configured to sequentially move scratch probe12 from one device 16 to other devices 16 so as to sequentially test theplurality of electronic device structures 16.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A method for measuring toughness of interfacial adhesion, the methodcomprising: applying a normal force with a probe to a surface of acoating joined to a major surface of a substrate of an electronicstructure, wherein the surface is substantially parallel to the majorsurface; applying a lateral force to the coating with the probe bylaterally moving a position of the probe relative to the major surfacesuch that the probe forms at least one delaminated region in the coatingas the position of the probe moves laterally across the major surface,the delaminated region having a starting point and an ending point;measuring a magnitude of the lateral force over time; determining atoughness of interfacial adhesion between the coating and the majorsurface based on changes in magnitude of the lateral force as theposition of the probe moves from the starting point to the ending point.2. The method of claim 1, wherein the probe comprises a configurationwhich is substantially symmetrical about a longitudinal axis.
 3. Themethod of claim 1, wherein the probe comprises a cono-sphericalconfiguration.
 4. The method of claim 1, further including: measuring anormal displacement of the probe relative to the major surface as theposition of the probe moves laterally relative to the major surface; anddetermining the starting point and the ending point based on the normaldisplacement.
 5. The method of claim 1, wherein the starting pointcorresponds to a point of initial fracture of the coating.
 6. The methodof claim 1, wherein the ending point corresponds to a point where aportion of coating separated from the major surface by the scratch tipto form the delaminated region ceases to separate from the majorsurface.
 7. The method of claim 1, wherein determining the toughness ofinterfacial adhesion further includes determining an amount ofinterfacial energy based on increases in magnitude of the lateral forceas the position of the probe moves from the starting point to the endingpoint, wherein the increases are relative to a magnitude of the lateralforce when the probe is at the starting point.
 8. The method of claim 1,wherein determining the toughness of interfacial adhesion furtherincludes: determining an area of the delaminated region; and dividingthe amount of interfacial energy by the area of the delaminated region.9. The method of claim 1, wherein applying the normal force furtherincludes applying the normal force at a substantially constantmagnitude.
 10. The method of claim 9, wherein applying the normal forceincludes applying at a substantially constant magnitude which causes theprobe to form a desired number of delaminated regions in a desireddistance across the major surface.
 11. The method of claim 1, whereinapplying the normal force further includes applying the normal force ata magnitude which increases over time.
 12. The method of claim 1,wherein applying the lateral force includes moving the position of theprobe such that the probe forms a series of delaminated regions in thecoating with each delaminated region having a beginning point and anending point.
 13. The method of claim 12, wherein determining atoughness of interfacial adhesion between the coating and major surfaceincludes: determining a toughness of interfacial adhesion for eachdelaminated region of the series of delaminated regions; and determininga toughness of interfacial adhesion between the coating and the majorsurface of the substrate of the electronic structure by averaging thetoughness of interfacial adhesion of a selected portion of the series ofdelaminated regions.
 14. A system for measuring a toughness ofinterfacial adhesion of coatings on electronic structures, comprising: aprobe; a controller configured to cause the probe to apply a normalforce to a surface of a coating applied to a major surface of asubstrate of an electronic structure, wherein the surface issubstantially parallel to the major surface, and configured to cause theprobe to apply a lateral force to the coating by laterally moving aposition of the probe relative to the surface so as to cause the probeto form at least one delaminated region in the coating, wherein thedelaminated region has a starting point and an ending point; a forcesensor configured to measure a magnitude of the lateral force over time;and an analyzer module configured to determine a toughness ofinterfacial adhesion between the coating and the major surface based onincreases in the measured magnitudes of the lateral force as the probemoves from the starting point to the ending point.
 15. The system ofclaim 14, wherein the controller is configured to measure a normaldisplacement of the probe relative to the surface as the position of theprobe moves laterally relative to the surface, and wherein the analyzermodule is configured to determine the starting point and the endingpoint based on the normal displacement.
 16. The system of claim 14,wherein the controller is configured to control and measure a lateralvelocity of the probe with respect to the electronic structure.
 17. Thesystem of claim 14, wherein the analyzer comprises a portion of thecontroller.
 18. The system of claim 14, wherein the probe comprises aprobe having a configuration which is substantially symmetrical about alongitudinal axis.
 19. The system of claim 14, wherein the probecomprises a probe having a cono-spherical configuration.
 20. The systemof claim 14, further including a holding device comprising a platformand a vacuum system is coupled to the platform and configured to createa vacuum via a plurality of perforations in the platform to secure theelectronic structure against the platform.
 21. The system of claim 14,further including a holding device comprising a magnetic platformconfigured to magnetically secure at least one electronic structure tothe magnetic platform.
 22. The system of claim 14, further comprising animaging device configured to provide an image of the coating, includingthe delaminated region.
 23. The system of claim 14, wherein the imagingdevice includes a measurement module configured to determine an area ofthe delaminated region.
 24. A method of measuring properties ofinterfacial adhesion, the method comprising: applying a normal force toa surface of a thin-film joined to a major surface of an electronicstructure, wherein the surface is substantially parallel to the majorsurface; applying a lateral force to the coating relative to the surfaceso as to separate a portion of the coating from the major surface toform a delaminated region, the delaminated region having a startingpoint and an ending point; measuring a magnitude of the lateral forceover time; and determining a toughness of interfacial adhesion betweenthe coating based on increases in the measured magnitudes of the lateralforce during a time period required to form the delaminated region fromthe starting point to the ending point, wherein the increases inmeasured magnitudes of the lateral force are relative to a measuredmagnitude of the lateral force at a time corresponding to the beginningof the time period.